Saturday Science – Our Visit to LIGO

The LIGO control room. These monitors – and more to the left and right plus the banks of monitors at the work stations – keep track of what's going inside the massive detector.
The LIGO control room. These monitors – and more to the left and right plus the banks of monitors at the work stations – keep track of what’s going inside the massive detector.

Tori and I spent Saturday afternoon touring LIGO. Let me explain.

We had been watching a series of science documentaries recently, geeking out over black holes and the like. There was one about gravity waves, which had been predicted by Einstein but which had never been observed, tiny ripples in space-time spreading across the universe from massive, unseen events.

Unseen, that is, until September 2015, when a gravity wave from an event that occurred about 130 million years ago, was detected.

And then they said the words that got our attention. The observation had been made by the two LIGOs, which had been painstakingly designed and built for that specific purpose – one in Hanford, Washington, and one in Livingston, Louisiana.

Quick check of the map – that was only an hour’s drive away! Quick check of the website – They have tours every third Saturday of the month!

The two LIGO tunnels – the second is visible in front of the tree line – converge on the main building, where a laser beam is split and sent shooting down both sides.
The two LIGO tunnels – the second is visible in front of the tree line – converge on the main building, where a laser beam is split and sent shooting down both sides.

LIGO stands for Laser Interferometer Gravity-wave Observatory. It is comprised of two long tunnels – each two and a half miles long – at right angles to each other. They form a big L. Inside is a long vacuum pipe, the most complete vacuum in the country. A laser beam is split, shoots down both pipes and is reflected back, where it is recombined. If nothing interferes, the two beams arrive at exactly the same time and cancel each other out.

 

One of LIGO's two tunnels – two and a half miles long – stretches into the distance.
One of LIGO’s two tunnels – two and a half miles long – stretches into the distance.

But Einstein had suggested that if a gravity wave happens by at the speed of light, it would cause one of the pipelines to contract ever so slightly and the other to expand by the same minute amount. The laser beam would be briefly misaligned, and that would register on the sensors.

The first gravity wave detected was caused by a pair of black holes colliding. Last week they detected a black hole swallowing a neutron star.

And not too long ago they hit the trifecta – detecting the collision of two neutron stars, an event that was also observed by gamma ray detectors and visual telescopes. In fact, LIGO detected the event first and immediately flooded the wires with a report of what they thought they had and where astronomers should point their instruments. And sure enough, there was a bright new object in that part of the sky.

The “control room” is filled with computer monitors, walls full of them and banks of them on the desks. And all of them are monitoring conditions inside the tunnels. They don’t show what’s being detected, because it happens so fast a human observer wouldn’t see anything. Instead the system records all the data and if an anomaly shows up it lets the humans know.

There are three such detectors in the world – the two LIGOs, 3,000 miles apart, run by a consortium led by Cal Tech, and a third, VIRGO, outside Pisa, Italy, run by a European science consortium. They share data and analysis and between them they act like the three legs of a GPS system, allowing scientists to determine where in the great vast universe the event took place.

What’s the point? I mean, seriously, what difference does it make? Decades went into designing and building the detectors – to what end? Well, it proves another part of Einstein’s theory, it helps us understand how the universe is built and how it works. Knowing things is better than not knowing them.

It also emphasizes how damn big the universe is. LIGO had been shut down for a while to tweak the system and improve its sensitivity. It is now detecting gravity waves coming from farther out than ever before, at a rate of almost one a day! There’s a lot going on out there. The universe is a big, violent place.

The Livingston facility also had a nice visitor center with plenty of hands-on science for kids, all of them hammering home lessons on light and sounds waves and kinetic energy. It was a fun afternoon of …

SCIENCE!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s